Wave signaling system



June H, 1929. ARMSTRONG 1,736,573

WAVE S IGNALING SYSTEM Filed Feb. 24, 1922 4 Sheets-Shee t 1- 11v ENTOR 9 5 N @mfiy m QQML WM y LATTORNEYS June 11, 1929. E, H ARMSTRONG flfififiETB WAVE SIGNALING SYSTEM Filed Feb. 24, 1922 4 Sheets-Sheet 2 Ideal 7 Actual FM XK W ENTOR ATTORNEYS June 11, 11929. E ARMSTRONG 1,716,573

/ WAVE SIGNAL-LNG SYSTEM Filed Feb. 24 1922 4 Sheets-Sheet 5 4? illil 59 ili 7 pm MMATTORNEx S June M, 1929.

E. H. ARMSTRONG WAVE SIGNALING SYSTEM Filed Feb. 24, 1922 4 Sheets-Sheet 4 Amplhqzi" Patented June 11, 1929.

, unirau STATES 'PATEN'r "GFFlCE.

EDWIN H. ARMSTRONG, O3 YONKERS, NEW YORK.

WAVE SIGNALING sys'rm.

Application filed February 24, 1922. Serial No. 588,856.

ception of signals, are greatly reduced. The

apparatus and circuit arrangement of the invention will be referred to as the heterodyne balance.

The fundamental principle underiliying the present invention is that of the di erential heterodyne balance described in my paper delivered before the Institute of Radio Engineers, on March 5, 1915, published in vol. 3, N o. 3, September 1915 of the Proceedings of the Institute of Radio Engineers. In this paper a radio receiving system is illustrated and described wherein the incoming high fre- 'quency signal oscillations are combined in two separate circuits with locally generated high frequency oscillations, and in such a manner that the beat or heterodyne currents produced in one circuit differ in phase by 180 from that produced in the other circuit. In this system suitable arrangements are p1%- vided for rectifying the two beat currents in separate detectors and the rectified currents are combined in the proper phase. Theoretically the signal should be augmented and the disturbances balanced out. Practical arrangements employing this system, however, have not been found to operate satisfactorily for reasons which will appear more fully hereinafter.

The present invention relates generally to improvements both in the method and apparatus for utilizing the above described principle, and it will be better understood by reference to the following description and accompanying drawings. In these drawings:

Fig. 1 illustrates a system adapted to operate in accordance with the disclosure of the aforementioned radio institute paper;

Fig. 2 shows a simplified schematic circuit arrangement the mode of operation of which is in accordance with the present invention;

- Fig. 3 illustrates schematically the character of the currents or oscillations which would theoretically exist in the various portions of the circuit arrangements of Fig. 1;

Fig. 4 shows ideal or-straight line law and actual or normal square law characteristic curves of detectors;

Fig. 5 illustrates a practical application of the present invention to the reception of weak I signals, for example, long distance or transoceanic signals; and I 1 Fig. 6 illustrates a system in which the process of heterodyne balancing is carried out in two stages (cascade) whereby certain aglvantages hereinafter explained are obtaina e.

The fundamental principle underlying the present invention will be understood by refer ence to Fig. 1., in which the antenna circuit 1--2, is divided into two equal branches 3, 4. To each branch is coupled secondariesfi and 6, respectively, having detectors 7 and'8 in series therewith. Each detector also has connected in series therewith the primaries of telephone transformers 9 and 10 respectively. The secondaries'll and 12 of those transformers are connected in series with the telephone receivers 13, with such polarity thatwhen there is no local oscillation in the system, the rectified currents cancel each other.

A source 14 of high frequency electromotive force is associated with the antenna circuit 1, 2, by means of coils 15 and 16, with such polarity as to cause the currents in the two branches to flow in opposite directionsthat is, so as to cause the current to flow up in one branch of the antenna circuit, when it is flowing down in the other The theory of the operation will be readily understood from the following analysis:

Assume the antenna circuit 1, 2 to be tuned to the incoming high frequency signal energy and the frequency of the electromotive force supplied from the source 14 to be adjusted at some frequency slightly different from the incoming signal so as to produce an audible beat tone; and providing the amplitude of the locally produced oscillations of the source 14 is adjusted to be equal to the amplitude of the incoming signal oscillations, the currents in the diflerent portions of the circuit arrangement of Fig. 1 will be substanthe rectified currents in the primaries 9 and lOas shown at 23 and 24; the current in the telephones 13 may be represented as at 25.

It will therefore be understood that by combining the incoming signal oscillations with the local oscillations in the manner described, the phase of the rectified currents are shifted rectifier characteristics. The recedingthe- 180 with, respect to each other and hence these two currents in the circuit contalning the telephones, are in phase and reinforce each other.

It should be observed that the reversal of phase by the combination of the incoming and local oscillations, can be produced only when the amplitude of the incomin oscillations is less than that of the local oscillations. When the amplitude of the incoming oscillations is reater than that of the local oscillations, on y components of the incoming oscillations equal in amplitude to the local oscillations can be reversed in phase and all of the incoming oscillations above this amplitude are accordingly cancelled out, Hence, on'account of their great amplitude in comparison with both the s1 al and the local oscillations, oscillations pro need by atmospheric disturbances or other types of interference are unable to combine with the local oscillations to produce beats. The interfering oscillations are, therefore, rectified substantially as they are and the two resulting rectifiedcurrents are then opposed in the circuit containing the telephones and cancel out with the exception of the com onent already mentioned, which is of negligible importance.

In the application of this principle to prac tice, a hitherto unsurmountable difiiculty has been encountered because of the shape of all ory assumes a straight line characteristicifor the detector that 1s, that the rectified anew frequency current is roportionahtothe amplitude of the high requency electromotive force impressed upon it.'- The actual characteristics of detectors follow the square law;

-nals are raised to the secon that is, the rectified current is proportional to a the s uare of the hi h frequency electromotive orce impresse upon, it. This results in two difliculties; one is the increased difficulty of balancing the rectified currents or disturbances against each other since the relative magnitude of these disturbances in the secondaries 11 and 12 with res ect to the sigpower. The

second difliculty may best be understood by reference to the graphic representationpf the ideal and actual characteristic shown in Fig. 4 at 26 and 27 respectively.

First assume a signal having an amplitude proportional to one (1). Then assume that this signal is combined with a local oscillation which also has an amplitude proportional to one (1) The resultant beat current fluctuates in amplitude between two (2) and zero (0) in each of the branches 3 and 4 and therefore the amplitude of the signal in the circuit containing the telephone will be pro ortional to two (2).

uppose now that a disturbing impulse arrives (for the most disturbing case) in phase with one branch of the antenna and 180 out of phase with the other branch' of theantenna 'tional to four (4).

proportional to the first power of the im-- pressed electromotive force var similarly between six (6) and four (4). T e net current in the circuit containing the telephones is, therefore, proportional to the difference of these two values, or to two (2).

Considering now the case of the practical detector in which the rectified current is proportional to the square of the impressed electromotive force; again, assume an arbitrary value of one (I for the amplitude of the signal and a simi ar value for the local oscillations. The voltage impressed upon the detector by the combination of these two oscillations varies between a maximum of two (2) and zero (0) in each of the branches of the antenna circuit. .The rectified current proportional to the square of these values varies between a maximum'of four (4; .and iaero. (0).,

The telephone current, there Now assume an interferin sewithan amplitude of five (5), the comblned IDCOIHlIlg is proper and local energies producing an feleetromog f tive force which variesbetwe'ena maximum of SIX (6) and a minimum of four (4) ,This" electromotive force is impressed upontheQdetector and, since the rectified current varies as the square of the impressed electromotive force, produces a rectified current which va- I ries between a maximum of thirty-six (36),

and a minimum of sixteen (16) in one of the detector circuits, while the current in the other detector circuit is varying in the opposite sense between sixteen (,16) and thirty-six (36). Hence the current in the telephone cirv cuit becomes proportional to twenty (20).- or

five times the amplitude of the signaling cure' rent. Since the assumed initial disturbance in the antenna was five times the signal strength, it is apparent that no gain has been 'made in eliminating the disturbance.

In accordance with the present invention,

the difliculties above described are overcome This straightens out and alters the characteristic of the rectifier after'a certain initial elec-' tromotive force has been im ressed thereupon and makes it approach t e ideal rectifier,

Secondly, the incoming signals are amplified sufliciently so that the initial bend in the rectifier characteristic is passed and rectification takes place on that-part of the characteristic curire which approximates the ideal. It will, therefore, be understood that the arrangement of Fig. 1 is modified in accordance with this invention to produce the arrangement illustrated in Fig. 2. It will be noted that the general arrangement is the same as in Fig. 1, except that an amplifier 30 of the high frequency waves is interposed between the antenna c1rcuit, 31, 32 and the balanced circuits 33, 34; and two high resistances 35, 36' are inserted in series respectively with the rectifiers 37 and 38.

In the practical application of the method and apparatus of this invention to the recep tion of weak long distance signals, for example, transoceanic signals and the like, an arrangement Such as that illustrated in Fig. 5 may be employed. It is advisable to use rect1- fiers of the valve type, preferably, the Fleming valve or two element vacuum tube; The resistance used in series with the rectifiers or detectors may be from one hundred thousand to two hundred thousand ohms. Extremely high amplification is necessary to produce an extremely high amplification, it'is advisabie to shield all parts of the apparatus, particularly the generator of the local oscillations. It is also very important to keep the local oscilla tions from entering in or effecting the work of the amplifier, i. e., prevent reaction on the input of the amplifier otherwise the local oscillations will be amplified to such an extent by the amplifier that the last tubes thereof will be overloaded and will not function properly.

In Fig. 5 the antenna 45,46 is coupled to amulti-stage amplifier 47, the number of stages depending on the initial strength of the signal. The two branch circuits 48, 49 each contain the coupling inductances 50, 51, respectively, the high resistances 52, 53 and the vacuum tube rectifiers 54, 55. Potentiometers 56 and 57 and telephone transformers 58 and 59 are also included in the two branch circuits respectively. The function of the potentiometer is to enable the adjustment of the the local source 63, rectified by the valves 54, 55, the rectified cur-rents being combined thru the transformersystems 58, 60 and 59, 61 and supplied to the telephones 62.

Where a single application of this principle is insufficient to overcome interference a casplanation: With this arrangement the incoming oscillations are received by antennae 64, 65 and are then amplified by the amplifier 66. These amplified oscillations are then applied to the two branch circuits 67, 68 and differentially combined with a local source 69. The frequency of this source is adjusted to produce a beat frequency which is above good audlbility. The combined currents are then rectified in accordance with the princi-- ples already explained by means of the rectifying systems 70, 72 and 71, 73 and the tWo rectified currents are their transferred by means of the transformers and 7 5 to the circuit 76 where the signalsare added cumulatively and the disturbances differentially. The resulting current which is of a lower frequency than the current in the antenna but a higher frequency than will give good audibility is then passed to an amplifier 77, amplified, and again applied to the balanced branch circuits 78, 79. In these circuits the currents are differentially combined with a local source 80 which is adjusted to give a beat frequency within the range of good audibility. The combined currents are then rectified by the rectifier systems 81, 83 and 82, 84, transferred to the telephone circuit by the transformers 85, 86, and combined in the telephones 87. It will be understood that the principle may be applied as many times as is desired. It will also be understood that the local current may be combined with. the signaling current in only one of the branch circuits without departing from the spirit of the invention although the results will be inferior to making the combination in both branches.

As in the usual case, the antenna of the radio system may be replaced by conducting lines if it' is desired to employ the invention in connection with carrier current systems.

What I claim isi 1. Apparatus for producing substantially unidirectional current from a source of alternating electromotive force comprising in combination, a rectifier having a nonlinear characteristic, a resistance connected to said rectifier for controlling the flow of current therethrough, and connections for impressing the electromotive force of said source with respect to the characteristic of said rectifier being such as to cause the rectified current to bear a substantially linear relationship with respect to said alternating electromotive force.

3. Means for producing from an applied alternating electromotive force a substantially unidirectional current substantially proportional to the first power of the said applied electromotive force comprising, in :2 -combination, a rectifier through which the current flows and which current is substantially proportional to the square of the difference of potential across the rectifier, and

means having a different voltage-current characteristic connected to said rectifier for offsetting the nonlinear characteristic of the rectifier. v

4. The method of improving the signal to disturbance ratio in a' wave signaling re-.

1 ceiving'system'which comprises causing the received energy to produce'a plurality of alternating voltages; adding a locally sup- 1 plied-alternating voltage to one of said prodnc'ed voltages-"while simultaneously sub 40 tracting a locally supplied alternating volt- 'i age,'j'of,-the same frequency as said first mentiqned. local y Supplied voltage, from [other of said first mentioned produced voltages; separately producing rectified cur- .rentseach proportional to the first power };'of a corresponding one of the combined volt-' Ina ceiving system which comprises causing thereceived energyto produce a plurality of alternating voltages; adding a locally sup- ,glie'dalternating voltage to one of said prouced voltages while simultaneously sub- I tracting'a locally supplied alternating volt- J ges; converting the rectified currents into ternatingcurrents; and combining 'thet. .;-'-last mentioned currents.

r *5. ,The method of improving the signal 1, L'to disturbance ratio in a wave signaling reage, of the same frequency as said first mentioned locally supplied voltage, from another of said first mentioned produced voltages; separately producing rectified currents each proportional to the first power of a corresponding one of the combined volt-- ages; converting the rectified currents into branch circuit, a second branch circuit,

means including a rectifier insaid second mentioned branch circuit for producing rectified current substantially proportional to the first power of the diflerence of potential across said second -mentioned branch circuit, means including a local source of oscillations for impressing alternating electromotive forces upon said branch circuits, a signal-indicating device, and means controlled by the rectified currents for operating said signal-indicating device.

"7. A wave si nal receiving system comprising in com ination, a branch circuit, means including a rectifier in said branch circuit for producing rectified current substantially proportional to the first power of flthe difference of potential acrosssaid branch circuit, a. second branch circuit, means including a rectifier in said secondmentioned branch circuit for producing rectified current substantially proportional to the first power of'the difference of potential across said second mentioned branch circuit, means for impressing locally generated oscillations upon the first mentioned branch circuit and do; impressing locally generated oscillations upon the second mentioned branch circuit but -substantially-opposite in phase to the .oscillationslocally supplied to the first men- .tioned branch circuit, a signal-indicating device, and means controlled by the rectified currents for operating said signal-indicating device. 7 I

In testimony whereof I afiix my signature.

EDWIN H. ARMSTRONG. 

